LG 42" 42LD550 start up.

[Pukehead]

My LG 42 LD550 started to glitch out. The screen flashed every 15 seconds like it was getting a bad signal. I turned it off and it would not turn back on. The red led just pulses. There is a blue led in the top corner, seen with the cover off, that lights up and then goes off. These are the voltages i recorded on the connector.

NC 0.1 / Error 2.3
12v 12.3 / P-dim 2.7
12v 12.3/ A-dim 2.68
12v 12.3/ inv on,off 0.05
-
-
3.5v 3.4/ 3.5v 3.4
3.5v 3.4/ 3.5v 3.4
-
20v 23.6/ 20v 23.6
On 3.2/ 20v 23.6

I charged the INV pin with 3v and the back light did not come on.

There is a back button on the main board that when pushed, the back lights flash for a second and then go back off.

Any advise would be much appreciated.

[nomoresonys]

Re: LG 42" 42LD550 start up.

Check the fuse on the inverter board.

[nomoresonys]

Re: LG 42" 42LD550 start up.

Can you do the test in #3 below? try to do it just as instructed. Be VERY CAREFUL what you touch on the HOT/DEADLY side of the powerboard, that connector is on the cold side.

[Pukehead]

Re: LG 42" 42LD550 start up.

Can you do the test in #3 below? try to do it just as instructed. Be VERY CAREFUL what you touch on the HOT/DEADLY side of the powerboard, that connector is on the cold side.

power on:

NC 0.1 / Error 2.3
12v 12.3 / P-dim 2.7
12v 12.3/ A-dim 2.68
12v 12.3/ inv on,off 0.05
-
-
3.5v 3.4/ 3.5v 3.4
3.5v 3.4/ 3.5v 3.4
-
20v 23.6/ 20v 23.6
On 3.2/ 20v 23.6


power Off

NC 0.0 / Error 0.0
12v 0.0 / P-dim 0.0
12v 0.0/ A-dim 0.0
12v 0.0/ inv on,off 0.00
-
-
3.5v 3.4/ 3.5v 3.4
3.5v 3.4/ 3.5v 3.4
-
20v 0.0/ 20v 0.0
On 0.0/ 20v 0.0

fuse on pwr board is good.

[nomoresonys]

Re: LG 42" 42LD550 start up.

" inv on,off 0.05" Needs to be 2.5 volts or more to turn on backlights, the inverter on signal comes from the mainboard so looks like a mainboard problem.

[Pukehead]

Re: LG 42" 42LD550 start up.

" inv on,off 0.05" Needs to be 2.5 volts or more to turn on backlights, the inverter on signal comes from the mainboard so looks like a mainboard problem.

Im thinking the same, but when i put 3v to the pin, power board side. Nothing happend.

[Pukehead]

Re: LG 42" 42LD550 start up.

Do you know what that little black button on the main board does? Cuz when i push it in, back lights come on for 1 second.

[nomoresonys]

Re: LG 42" 42LD550 start up.

You can jumper the powerboard to test it and the backlights, you MUST disconnect the cable from the powerboard to the mainboard for the test, I am not exactly sure which pins need jumpered on this paticular board tho.

[Pukehead]

Re: LG 42" 42LD550 start up.

i will try it with the connector off.

[nomoresonys]

Re: LG 42" 42LD550 start up.

It is suggested to use a resistor in case you get the wrong pins, so will be resistor to go from standby pin to power on then a resistor from standby pin to bl-on and might also need another to go standby to A-DIM and another from standby to P-DIM, not sure, so could need to use as many as 4 resistors to jumper standby pin to those.

[Pukehead]

Re: LG 42" 42LD550 start up.

Without the connector plugged in, I have no voltages on any pin. The TV wont even go into standyby.

[budm]

Re: LG 42" 42LD550 start up.

Without the connector plugged in, I have no voltages on any pin. The TV wont even go into standyby.

No Voltage On the power supply connector?
We are testing the power supply board without Main board connected, not testing the main board.

[Pukehead]

Re: LG 42" 42LD550 start up.

No Voltage On the power supply connector?
We are testing the power supply board without Main board connected, not testing the main board.

Im not sure what board i should be testing now.

[Pukehead]

Re: LG 42" 42LD550 start up.

BudM do know what that green and black button on the main board does? after pushing the green button and then the black button, the back light comes on for a second. Then the TV shuts down back into standby.

[budm]

Re: LG 42" 42LD550 start up.

Im not sure what board i should be testing now.

Post #6 ~ 11 are for testing the power supply board using resistors to force on the power supply and backlights.

[Pukehead]

Re: LG 42" 42LD550 start up.

What size resistors would you suggest using?

[budm]

Re: LG 42" 42LD550 start up.

Any value between 470 ~ 1000 Ohms 1/4 W will be fine.

[Pukehead]

Re: LG 42" 42LD550 start up.

OK. ill see what i have laying around.

[Pukehead]

Re: LG 42" 42LD550 start up.





So I was able to charge the INV/ CTR pin with 2+volts and the back-light comes on. So the power board is working. The red led on front bezel still pulses tho.

The highlighted switch in the schematic when pushed enables the back-lights to flash for one second when the INV/ CTR pin is not charged. I think the issue is somewhere associate in this circuit, but im still not sure.

[budm]

Re: LG 42" 42LD550 start up.

Remove all the test resistors then connect all the connector back in place then check the resistance between GND and INV on pin to see what it shows.